Conventionally, for treating a cancer by a radiation ray, an X-ray, a gamma ray and an electron beam, etc., have been applied, and in recent years, a charged particle beam irradiator which treats a cancer, etc., using a high energy charged particle beam (such as a carbon ion beam, etc.,) accelerated by an accelerator has been developed (refer to non-patent document 1).
Here, a description is given on a charged particle beam irradiator 100 as described above, referring to FIG. 4 and FIG. 5. As illustrated in FIG. 4, charged particles which are accelerated with high energy while traveling through an accelerator (not illustrated) such as a synchrotron, etc., enter a final bending electromagnet, after traveling through quadrupole electromagnets 110, 111, 112, etc. The quadrupole electromagnets 110, 111, 112 are converging electromagnets which suppress the divergence of the beam traveling through a beam transfer tube 114, and the final bending electromagnet bends charged particles toward a target. Then, the charged particles which enter the final bending electromagnet 113 travel in the bending electromagnet 113 drawing a curve in an arc shape.
Next, as illustrated in FIG. 4 and FIG. 5, the charged particle beam travels through an X-direction dipole electromagnet (an irradiation field forming electromagnet) 115 which scans the beam in the X-direction which is parallel to a plane including a bending trajectory of the beam traveling through the final bending electromagnet 113 and being perpendicular to the direction of the beam traveling, and further travels through a Y-direction dipole electromagnet (an irradiation field forming electromagnet) 116 which scans the beam in the Y-direction being perpendicular to the direction of the beam traveling and the X-direction, and then a target 117 is irradiated with the charged particle beam. Otherwise, a configuration is possible where the charged particle beam travels through an X-direction dipole electromagnet after traveling through a Y-direction dipole electromagnet.
Meanwhile, in treating a cancer using such a charged particle beam irradiator 100, 180 degree—or 360 degree—rotation irradiation centering around the cancer cells is preferable, in order to increase an efficiency of the cancer treatment and to relieve the patient from pain. Accordingly, if a charged particle beam is applied in cancer treatment, a rotary gantry which irradiates a patient lying on a bed with a proton beam from the circumference is used widely (refer to patent document 1).
Non-patent document 1: ‘Wobbler facility for biological experiments’ Timothy R. Renner and William T. Chu, Medical Physics, Vol. 14, pp. 825-834 (1987)
Patent document 1: Japanese Laid Open Patent Application Publication No. 1996-257148 (paragraphs 0012-0013 and FIG. 1).
Meanwhile, in a conventional charged particle beam irradiator 100, two dipole electromagnets of an X-direction dipole electromagnet 115 and a Y-direction dipole electromagnet 116 are disposed in a downstream side of a final bending electromagnet 113. Here, the X-direction dipole electromagnet 115 and Y-direction dipole electromagnet 116 are required to generate an electromagnetic field larger by a factor of three than an electromagnetic field applied for bending a proton beam, because ions such as a carbon ion, etc., are heavier than proton. Further, for treating a cancer, etc., the charged particle beam with a diameter of about 1 cm supplied from an accelerator is required to be enlarged to a size which can form an irradiation field of about 20 cm in diameter. Therefore, in order to enlarge a charged particle beam composed of a carbon ion beam, etc., using the X-direction and the Y-direction dipole electromagnets, a length of irradiating port (a length between either the X-direction dipole electromagnet 115 or the Y-direction dipole electromagnet 116 disposed in an upstream side and the target 117), is needed to be lengthened further. If a charged carbon beam (a carbon ion beam) is applied, a rather long port length around 5.5 m is needed at the shortest, and thereby, a problem that the apparatus gets bigger is raised.
If the charged particle beam irradiator as described above is applied to a rotary gantry described in patent document 1, a space needed for driving the rotary gantry should be about 18×9×9×π m3, for example, and thereby, a problem that the apparatus gets bigger is raised.
Accordingly, a charged particle beam irradiator and a rotary gantry which come in a reduced size as a whole have been desired.